I had the same dilemma a few months ago. Not only I was presenting the same work, but the conferences were a couple of weeks apart from one other. Perhaps you could consider approaching them with different purposes. This will change your abstract and your presentation. So for example, one would concentrate on the results, the other would introduce the project (the poster one probably), and the other one could talk about your PhD research but use this particular project as recent findings. Because you are talking to different audiences, it is sometimes necessary to present the same findings at different settings.